Recently, improvement in fuel efficiency of automobiles, engine room narrowing, and cost reduction of vehicles are advancing in an automobile industry. Electronic control units for controlling engines, transmissions, etc are provided in the vehicle and further reduction in size, weight, and cost are also required in these electronic control units.
Meanwhile, the electronic control units tend to be directly attached to a vehicle body side in an inside of the engine room from an inside of a vehicle passenger compartment, and further to the engines, the transmissions, or the like to be controlled. Therefore, a housing coping with a mounting environment, such as a waterproof structure, a corrosion resistant structure, and coping with high temperature is required in the electronic control units. Accordingly, the electronic control units waterproof an electronic circuit board by interposing a seal material on a peripheral portion or the like of an exterior member forming the housing. A silicone based adhesive and a rubber packing are common as the seal material. However, the silicone based adhesives or the rubber packing is a material with high cost, and wide area for sealing is required. Accordingly, an example of a method for promoting compactness, weight reduction and cost reduction of the electronic control units, includes reduction of the seal material.
As a background art of the present invention, there is a JP-A-2013-69735 (PTL 1). A seal structure of an electronic control device that includes a housing seal portion which is provided in an endless annular shape over the entirety of the periphery of a mating surface portion between a peripheral portion of an upper surface side of a case and a peripheral portion of a lower surface side of a cover, and a connector seal portion which is provided in an endless annular shape over the entirety of the periphery of a joining surface portion between an outer peripheral surface of a connector and an inner peripheral surface of a window portion of the housing (case and cover) is described in paragraphs 0021 to 0027 of PTL 1. The housing seal portion is configured by a seal groove having a U-shaped cross section provided on a case side and a ridge which is provided on lower surface sides of the connector and the cover, is fitted into the seal groove with a predetermined gap, and has a strip shape which has a rectangular-shaped cross section. Then, the gap between the seal groove and the ridge is filled with a seal agent. At this time, the depths and the widths of the seal groove and the ridge are set to be substantially constant over the entirety of the periphery so as to secure a constant seal length. The seal groove and the ridge are also provided in the connector seal portion, as in the housing seal portion. The ridge is provided on the connector side in lower surface side of the connector, and the seal groove is formed on the connector side in a portion excluding the lower surface side thereof. At this time, the seal groove is formed on the lower surface side of the connector so that the depth thereof is deep and the groove width thereof is narrow. In addition, the seal groove is formed on the upper surface side of the connector so that the depth thereof is shallow and the groove width thereof is wide. Accordingly, a seal length of the connector seal portion is set to be constant over the entirety of the periphery thereof. Further, the provision of a fitting structure between an auxiliary seal groove and an auxiliary ridge is described so that the seal length is secured at a joint portion between the connector seal portion and the housing seal portion in paragraphs 0033 to 0038 of PTL 1.
In addition, a vehicle-mounted electronic equipment using a waterproof seal in which an inorganic filler and a water absorbing or hygroscopic organic filler are blended in a resin which reacts with moisture in the atmosphere and is cured by crosslink of polymers with each other is described as a waterproof seal in the abstract of JP-A-2014-3206 (PTL 2).